efi_loader: fix incorrect use of EFI_EXIT()
efi_get_variable_common() does not use EFI_ENTRY(). So we should not use
EFI_EXIT() either.
Fixes: 767f6eeb01d3 ("efi_loader: variable: support variable authentication")
Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>