efi_loader: fix entry count in bootmgr

Since commit 914df75b ("efi_loader: fix EFI entry counting")
entry_count is already set to 1 before efi_bootmgr_load() is called. So we
should not increment it when entering the function.

Without the patch an assert error occurs in efi_get_variable() if DEBUG is
defined.

Fixes: 914df75b ("efi_loader: fix EFI entry counting")
Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>