drivers/firmware/memmap.c: pass the correct argument to firmware_map_find_entry_bootmem()

firmware_map_add_hotplug() calls firmware_map_find_entry_bootmem() to
get free firmware_map_entry.  But end arguments is not correct.  So
firmware_map_find_entry_bootmem() cannot not find firmware_map_entry.

The patch passes the correct end argument to firmware_map_find_entry_bootmem().

Signed-off-by: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
Cc: Santosh Shilimkar <santosh.shilimkar@ti.com>
Cc: Toshi Kani <toshi.kani@hp.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>