efi: Fix comment for efi_mem_type() wrt absent physical addresses

A previous commit f99afd0 ("efi: Update efi_mem_type() to return an
error rather than 0") changed the return value from EFI_RESERVED_TYPE to
-EINVAL when the searched physical address is not present in any memory
descriptor. But the comment preceding the function never changed. Let's
change the comment now to reflect the new return value -EINVAL.

Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20200113172245.27925-10-ardb@kernel.org

drivers/firmware/efi/efi.c

@@ -908,7 +908,7 @@ u64 efi_mem_attributes(unsigned long phys_addr)
  *
  * Search in the EFI memory map for the region covering @phys_addr.
  * Returns the EFI memory type if the region was found in the memory
- * map, EFI_RESERVED_TYPE (zero) otherwise.
+ * map, -EINVAL otherwise.
  */
 int efi_mem_type(unsigned long phys_addr)
 {