staging: fbtft: Use sysfs_emit_at() to print to sysfs file

This scnprintf() uses the wrong limit.  It should be "PAGE_SIZE - len"
instead of just PAGE_SIZE.  We're not going to hit the limit in real
life since we are printing at most FBTFT_GAMMA_MAX_VALUES_TOTAL (128)
u32 values, however, it's still worth fixing.

Use sysfs_emit_at() to fix this since this is a sysfs file.

Fixes: c296d5f995 ("staging: fbtft: core support")
Signed-off-by: Dan Carpenter <[email protected]>
Reviewed-by: Andy Shevchenko <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>

drivers/staging/fbtft/fbtft-sysfs.c

@@ -98,7 +98,7 @@ sprintf_gamma(struct fbtft_par *par, u32 *curves, char *buf)
 	mutex_lock(&par->gamma.lock);
 	for (i = 0; i < par->gamma.num_curves; i++) {
 		for (j = 0; j < par->gamma.num_values; j++)
-			len += scnprintf(&buf[len], PAGE_SIZE,
+			len += sysfs_emit_at(buf, len,
 			     "%04x ", curves[i * par->gamma.num_values + j]);
 		buf[len - 1] = '\n';
 	}