memory.h: fix typos in comments

Signed-off-by: Li Qiang <liq3ea@gmail.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-Id: <1539080467-2976-1-git-send-email-liq3ea@gmail.com>
[lv: s/types/typos/]
Signed-off-by: Laurent Vivier <laurent@vivier.eu>

include/exec/memory.h

@@ -935,7 +935,7 @@ uint64_t memory_region_size(MemoryRegion *mr);
 /**
  * memory_region_is_ram: check whether a memory region is random access
  *
- * Returns %true is a memory region is random access.
+ * Returns %true if a memory region is random access.
  *
  * @mr: the memory region being queried
  */
@@ -947,7 +947,7 @@ static inline bool memory_region_is_ram(MemoryRegion *mr)
 /**
  * memory_region_is_ram_device: check whether a memory region is a ram device
  *
- * Returns %true is a memory region is a device backed ram region
+ * Returns %true if a memory region is a device backed ram region
  *
  * @mr: the memory region being queried
  */
@@ -1161,7 +1161,7 @@ uint8_t memory_region_get_dirty_log_mask(MemoryRegion *mr);
 /**
  * memory_region_is_rom: check whether a memory region is ROM
  *
- * Returns %true is a memory region is read-only memory.
+ * Returns %true if a memory region is read-only memory.
  *
  * @mr: the memory region being queried
  */