target/dsp563xx: fix scan-build warning

Scan-build triggers a warning:
	Unix API: Allocator sizeof operand mismatch
	dsp563xx.c:2143 Result of 'calloc' is converted to a pointer
		of type 'uint8_t', which is incompatible with sizeof
		 operand type 'uint32_t'

It's a false positive because calloc() is properly used in this
case, as the uint8_t array is used in blocks of 4 elements to read
or write uint32_t values.

Either
	calloc(sizeof(uint32_t), count);
and
	malloc(count * sizeof(uint32_t));
keep triggering the same warning.

Drop the warning by using the constant '4' as size of uint32_t, as
already used few lines below.

Change-Id: I5bb1ece177774eefdc5d9cd049338f8f2be87cd7
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/7203
Tested-by: jenkins
Reviewed-by: Andreas Fritiofson <andreas.fritiofson@gmail.com>

src/target/dsp563xx.c

@@ -2140,7 +2140,7 @@ COMMAND_HANDLER(dsp563xx_mem_command)
 			COMMAND_PARSE_NUMBER(u32, CMD_ARGV[1], count);
 	}
 
-	buffer = calloc(count, sizeof(uint32_t));
+	buffer = calloc(count, 4);
 
 	if (read_mem == 1) {
 		err = dsp563xx_read_memory(target, mem_type, address, sizeof(uint32_t),