loader: Fix incorrect parameter name in load_image_mr() macro

Fix a typo in the load_image_mr() macro: 'mr' was written when
the parameter name is '_mr'. (This had no visible effects since
the single use of the macro used 'mr' as the argument.)

Fixes 76151cac "loader: Add
load_image_mr() to load ROM image to a MemoryRegion"
Signed-off-by: NJens Wiklander <jens.wiklander@linaro.org>
Reviewed-by: NPeter Maydell <peter.maydell@linaro.org>
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>

include/hw/loader.h

@@ -137,7 +137,7 @@ void hmp_info_roms(Monitor *mon, const QDict *qdict);
 #define rom_add_blob_fixed(_f, _b, _l, _a)      \
     rom_add_blob(_f, _b, _l, _l, _a, NULL, NULL, NULL)
 #define rom_add_file_mr(_f, _mr, _i)            \
-    rom_add_file(_f, NULL, 0, _i, false, mr)
+    rom_add_file(_f, NULL, 0, _i, false, _mr)
 
 #define PC_ROM_MIN_VGA     0xc0000
 #define PC_ROM_MIN_OPTION  0xc8000