bpf: Fix warning for cast from restricted gfp_t in verifier

This fixes the sparse warning reported by the kernel test robot:

kernel/bpf/verifier.c:13499:47: sparse: warning: cast from restricted gfp_t
kernel/bpf/verifier.c:13501:47: sparse: warning: cast from restricted gfp_t

This fix can be verified locally by running:
1) wget
https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross


-O make.cross

2) chmod +x ~/bin/make.cross

3) COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-11.2.0 ./make.cross
C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__'

Fixes: b00fa38a ("bpf: Enable non-atomic allocations in local storage")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20220321185802.824223-1-joannekoong@fb.com