efivars: don't bother with realloc() if we have no interest in the old data

We shouldn't ask glibc to keep the old data around (which realloc() is
about), given we overwrite it entirely anyway. Let's hence speed things
up here, and allow glibc to just allocate a new block for us (and
shorten the code a bit)

src/basic/efivars.c

@@ -81,10 +81,10 @@ int efi_get_variable(
                 }
 
                 /* We want +1 for the read call, and +3 for the additional terminating bytes added below. */
-                char *t = realloc(buf, (size_t) st.st_size + MAX(1, 3));
-                if (!t)
+                free(buf);
+                buf = malloc((size_t) st.st_size + MAX(1, 3));
+                if (!buf)
                         return -ENOMEM;
-                buf = t;
 
                 const struct iovec iov[] = {
                         { &attr, sizeof(attr) },