bootmem: Fix the short description of reserve_bootmem()

It marks pages as reserved, as the long description says.

Signed-off-by: Javi Merino <javi.merino@arm.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
diff --git a/mm/bootmem.c b/mm/bootmem.c
index bcb63ac..f468185 100644
--- a/mm/bootmem.c
+++ b/mm/bootmem.c
@@ -419,7 +419,7 @@
 }
 
 /**
- * reserve_bootmem - mark a page range as usable
+ * reserve_bootmem - mark a page range as reserved
  * @addr: starting address of the range
  * @size: size of the range in bytes
  * @flags: reservation flags (see linux/bootmem.h)