include/linux/memblock.h: fix minor typo and unclear comment

Fix a minor typo "usabe->usable" for the current discription of member
variable "memory" in struct memblock.

BTW, I think it's unclear the member variable "base" in struct
memblock_type is currently described as the physical address of memory
region, change it to base address of the region is clearer since the
variable is decorated as phys_addr_t.
Signed-off-by: chenqiwu <chenqiwu@xiaomi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Mike Rapoport <rppt@linux.ibm.com>
Link: http://lkml.kernel.org/r/1588846952-32166-1-git-send-email-qiwuchen55@gmail.comSigned-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/memblock.h

@@ -41,7 +41,7 @@ enum memblock_flags {
 
 /**
  * struct memblock_region - represents a memory region
- * @base: physical address of the region
+ * @base: base address of the region
  * @size: size of the region
  * @flags: memory region attributes
  * @nid: NUMA node id
@@ -75,7 +75,7 @@ struct memblock_type {
  * struct memblock - memblock allocator metadata
  * @bottom_up: is bottom up direction?
  * @current_limit: physical address of the current allocation limit
- * @memory: usabe memory regions
+ * @memory: usable memory regions
  * @reserved: reserved memory regions
  * @physmem: all physical memory
  */