requirements: bump up cffi to 1.14.5

requirements: bump up cffi to 1.14.5

Needs for run on Big Sur with python3.9 from brew and addresses
building error for cffi wheel:

    clang -Wno-unused-result -Wsign-compare -Wunreachable-code -fno-common -dynamic -DNDEBUG -g -fwrapv -O3 -Wall -isysroot /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk -DUSE__THREAD -DHAVE_SYNC_SYNCHRONIZE -I/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/ffi -I/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/ffi -I/opt/homebrew/include -I/opt/homebrew/opt/openssl@1.1/include -I/opt/homebrew/opt/sqlite/include -I/opt/homebrew/opt/tcl-tk/include -I/Users/kyr/kshtsk/teuthology/virtualenv/include -I/opt/homebrew/Cellar/python@3.9/3.9.2_1/Frameworks/Python.framework/Versions/3.9/include/python3.9 -c c/_cffi_backend.c -o build/temp.macosx-11-arm64-3.9/c/_cffi_backend.o
    c/_cffi_backend.c:6185:5: warning: 'PyEval_InitThreads' is deprecated [-Wdeprecated-declarations]
        PyEval_InitThreads();
        ^
    /opt/homebrew/Cellar/python@3.9/3.9.2_1/Frameworks/Python.framework/Versions/3.9/include/python3.9/ceval.h:130:1: note: 'PyEval_InitThreads' has been explicitly marked deprecated here
    Py_DEPRECATED(3.9) PyAPI_FUNC(void) PyEval_InitThreads(void);
    ^
    /opt/homebrew/Cellar/python@3.9/3.9.2_1/Frameworks/Python.framework/Versions/3.9/include/python3.9/pyport.h:508:54: note: expanded from macro 'Py_DEPRECATED'
    #define Py_DEPRECATED(VERSION_UNUSED) __attribute__((__deprecated__))
                                                         ^
    c/_cffi_backend.c:6245:9: error: implicit declaration of function 'ffi_prep_closure' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
        if (ffi_prep_closure(closure, &cif_descr->cif,
            ^
    1 warning and 1 error generated.
    error: command '/usr/bin/clang' failed with exit code 1

Signed-off-by: Kyr Shatskyy <kyrylo.shatskyy@suse.com>