fbdev: sisfb: Fix strbuf array overflow

In the Linux kernel, the following vulnerability has been resolved: fbdev: sisfb: Fix strbuf array overflow The values of the variables xres and yres are placed in strbuf. These variables are obtained from strbuf1. The strbuf1 array contains digit characters and a space if the array contains non-digit characters. Then, when executing sprintf(strbuf, "%ux%ux8", xres, yres); more than 16 bytes will be written to strbuf. It is suggested to increase the size of the strbuf array to 24. Found by Linux Verification Center (linuxtesting.org) with SVACE.