gr_rasta_tmtc.c: Unchecked return value from library error spotted by Coverity

[Ryan Long]

CID 1399771: Unchecked return value from library in gr_rasta_tmtc_init1().

588        strcpy(priv->prefix, "/dev/rastatmtc0");
589        priv->prefix[14] += dev->minor_drv;
   CID 1399771 (#1 of 1): Unchecked return value from library (CHECKED_RETURN)2. check_return: Calling mkdir(priv->prefix, 511U) without checking return value. This library function may fail and return an error code. [Note: The source code implementation of the function has been overridden by a builtin model.]
590        mkdir(priv->prefix, S_IRWXU | S_IRWXG | S_IRWXO);
591        priv->prefix[15] = '/';
592        priv->prefix[16] = '\0';

[Ryan Long <ryan.long@…>]

In 17d525b5/rtems:

gr_rasta_tmtc.c: Fix Unchecked return value from library (CID #1399771)

CID 1399771: Unchecked return value from library in gr_rasta_tmtc_init1().

Closes #4286