libc: minimal: ctype: use unsigned int instead of unsigned

The "check warns" workflow in CI warned over the use of `unsigned` as a
shorthand for `unsigned int` in several locations in
`lib/libc/minimal/include/ctype.h`.

```
 UNSPECIFIED_INT: Prefer 'unsigned int' to bare use of 'unsigned'
File:lib/libc/minimal/include/ctype.h
```

Adjust `unsigned` to `unsigned int` to avoid linter warnings.

Signed-off-by: Chris Friedt <[email protected]>

Author: Chris Friedt

lib/libc/minimal/include/ctype.h

@@ -15,42 +15,42 @@ extern "C" {
 
 static inline int isupper(int a)
 {
-	return (int)(((unsigned)(a)-(unsigned)'A') < 26U);
+	return (int)(((unsigned int)(a)-(unsigned int)'A') < 26U);
 }
 
 static inline int isalpha(int c)
 {
-	return (int)((((unsigned)c|32u)-(unsigned)'a') < 26U);
+	return (int)((((unsigned int)c|32u)-(unsigned int)'a') < 26U);
 }
 
 static inline int isspace(int c)
 {
-	return (int)(c == (int)' ' || ((unsigned)c-(unsigned)'\t') < 5U);
+	return (int)(c == (int)' ' || ((unsigned int)c-(unsigned int)'\t') < 5U);
 }
 
 static inline int isgraph(int c)
 {
-	return (int)((((unsigned)c) > ' ') &&
-			(((unsigned)c) <= (unsigned)'~'));
+	return (int)((((unsigned int)c) > ' ') &&
+			(((unsigned int)c) <= (unsigned int)'~'));
 }
 
 static inline int isprint(int c)
 {
-	return (int)((((unsigned)c) >= ' ') &&
-			(((unsigned)c) <= (unsigned)'~'));
+	return (int)((((unsigned int)c) >= ' ') &&
+			(((unsigned int)c) <= (unsigned int)'~'));
 }
 
 static inline int isdigit(int a)
 {
-	return (int)(((unsigned)(a)-(unsigned)'0') < 10U);
+	return (int)(((unsigned int)(a)-(unsigned int)'0') < 10U);
 }
 
 static inline int isxdigit(int a)
 {
 	unsigned int ua = (unsigned int)a;
 
-	return (int)(((ua - (unsigned)'0') < 10U) ||
-			((ua | 32U) - (unsigned)'a' < 6U));
+	return (int)(((ua - (unsigned int)'0') < 10U) ||
+			((ua | 32U) - (unsigned int)'a' < 6U));
 }
 
 static inline int tolower(int chr)