measure: fix the failures of compare_reported_pcr_nr()

measure: fix the failures of compare_reported_pcr_nr()

EFI_LOADER_VARIABLE() already applies to the stringify to construct the
path of EFI variable in efivars, so it is wrong to enclose the name of
EFI variable with the quotes. Otherwise, the following errors are
reported.

Reading EFI variable /sys/firmware/efi/efivars/StubFeatures-4a67b082-0a4c-41cf-b6c7-440b29bb8c4f.
Reading EFI variable /sys/firmware/efi/efivars/"StubPcrKernelImage"-4a67b082-0a4c-41cf-b6c7-440b29bb8c4f.
open("/sys/firmware/efi/efivars/"StubPcrKernelImage"-4a67b082-0a4c-41cf-b6c7-440b29bb8c4f") failed: No such file or directory
Reading EFI variable /sys/firmware/efi/efivars/"StubPcrKernelParameters"-4a67b082-0a4c-41cf-b6c7-440b29bb8c4f.
open("/sys/firmware/efi/efivars/"StubPcrKernelParameters"-4a67b082-0a4c-41cf-b6c7-440b29bb8c4f") failed: No such file or directory
Reading EFI variable /sys/firmware/efi/efivars/"StubPcrInitRDSysExts"-4a67b082-0a4c-41cf-b6c7-440b29bb8c4f.
open("/sys/firmware/efi/efivars/"StubPcrInitRDSysExts"-4a67b082-0a4c-41cf-b6c7-440b29bb8c4f") failed: No such file or directory

Signed-off-by: Jia Zhang <zhang.jia@linux.alibaba.com>