gr_tmtc_1553.c: Unchecked return value from library error spotted by Coverity

[Ryan Long]

CID 1399785: Unchecked return value from library in gr_tmtc_1553_init1().

315        strcpy(priv->prefix, "/dev/tmtc1553_0");
316        priv->prefix[14] += dev->minor_drv;
   CID 1399785 (#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.]
317        mkdir(priv->prefix, S_IRWXU | S_IRWXG | S_IRWXO);
318        priv->prefix[15] = '/';
319        priv->prefix[16] = '\0';

[Ryan Long <ryan.long@…>]

In 5f0a7ceb/rtems:

gr_tmtc_1553.c: Unchecked return value from library (CID #1399785)

CID 1399785: Unchecked return value from library in gr_tmtc_1553_init1().

Closes #4289